ENGR00269616 mx6: Unexpected enter WAIT mode cause IPU underrun

ENGR00269616 mx6: Unexpected enter WAIT mode cause IPU underrun

CCM state machine has restriction that, everytime enable
LPM mode, we need to make sure last wakeup from LPM mode
is a dsm_wakeup_signal, which means the wakeup source
must be seen by GPC, then CCM will clean its state machine
and re-sample necessary signal to decide whether it can
enter LPM mode. Here we use the forever pending irq #125,
unmask it before we enable LPM mode and mask it after LPM
is enabled, this flow will make sure CCM state machine in
reliable state before we enter LPM mode.

Signed-off-by: Anson Huang <b20788@freescale.com>